Allowance for Loan Losses and Credit Quality of Loans, Credit Quality by Loan Class (Details) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 5,967,809	$ 5,883,133
Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,617,111	2,589,707
Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,138,877	2,096,646
Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,211,821	1,196,780
Originated Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	5,376,887	5,271,619
Originated Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,337,481	2,303,978
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,937,559	1,903,057
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,838,212	1,810,122
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	33,980	32,053
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65,359	60,874
Originated Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8	8
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	656,511	644,318
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	614,475	604,405
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	14,130	9,726
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	27,906	30,187
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,216,746	1,194,897
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,161,375	1,144,832
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	19,483	21,587
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	35,888	28,478
Originated Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	34,383	34,624
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	33,744	33,565
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1	311
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	630	740
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	8	8
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	29,919	29,218
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	28,618	27,320
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	366	429
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	935	1,469
Originated Loans [Member] | Commercial Credit Exposure [Member] | Agricultural Real Estate [Member] | Doubtful [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	0	0
Originated Loans [Member] | Commercial Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	399,922	400,921
Originated Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	399,922	400,921
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	386,194	386,397
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	13,728	14,524
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	399,922	400,921
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	386,194	386,397
Originated Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	13,728	14,524
Originated Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,052,568	2,001,219
Originated Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,045,193	1,991,910
Originated Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,375	9,309
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,536,349	1,477,250
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,533,133	1,473,193
Originated Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,216	4,057
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	457,280	464,715
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	453,296	459,540
Originated Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,984	5,175
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	58,939	59,254
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	58,764	59,177
Originated Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	175	77
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	986,838	966,422
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	979,685	958,013
Originated Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	7,153	8,409
Acquired Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	590,922	611,514
Acquired Loans [Member] | Commercial Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	279,630	285,729
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	233,857	235,934
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	217,711	222,112
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	4,679	2,976
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Total Commercial and Agricultural [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	11,467	10,846
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65,412	68,991
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	61,898	67,241
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,824	802
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	1,690	948
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	168,445	166,943
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	155,813	154,871
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Special Mention [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	2,855	2,174
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Commercial Real Estate [Member] | Substandard [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	9,777	9,898
Acquired Loans [Member] | Commercial Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,773	49,795
Acquired Loans [Member] | Business Banking Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,773	49,795
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42,271	46,032
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,502	3,763
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	45,773	49,795
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Non-classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	42,271	46,032
Acquired Loans [Member] | Business Banking Credit Exposure [Member] | Business Banking [Member] | Classified [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,502	3,763
Acquired Loans [Member] | Consumer Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	86,309	95,427
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	85,814	94,822
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	495	605
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	21,847	27,775
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	21,767	27,670
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Indirect [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	80	105
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	60,928	63,727
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	60,578	63,270
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Home Equity [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	350	457
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,534	3,925
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	3,469	3,882
Acquired Loans [Member] | Consumer Credit Exposure [Member] | Direct [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	65	43
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	224,983	230,358
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Performing [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	222,329	227,448
Acquired Loans [Member] | Residential Mortgage Credit Exposure [Member] | Nonperforming [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable	$ 2,654	$ 2,910